Improvement in screw-propellers



2 Sheets-Sheet 1 N. A. PATTERSON.

Screw-Propellers.

Patented August 26, 18 73.

WITNESSES:

INVENTOR:

r I I fltiorneys.

2Sheets--Sheet2. N. A. PATTERSON.

Screw-Propellers.

N0. l42,269. Patented August2 6,1873.

WITNESSES: INVENTOR:

. tudinal direction coincident with NEwToN A. PATTERSON, OF CLEVELAND, TENNESSEE.

EMPROVEMENT IN SCREW-PROPELLERS.

Specification forming part of Letters Patent No. 142,269, dated August 26, 1873; application filed June 6,1873.

To all whom it may concern:

Be it known that I, NEwToN ALEXANDER PATTERSON, of the city of Cleveland, in the county of Bradley, in the State of Tennessee, United States of America, have invented certain Improvements in Propellers, of which the following is a specification:

The primary object of this invention is to produce a propeller adapted, by the peculiar formation of its blades, to impart to the water in which it turns a longitudinal motion in a direction coincident or parallel with the axis of the screw, avoiding lateral or tangential motion. To this end theblades are constructed of concavo-convex form. To render the concavo-convex blades more effective, it is preferred to form them with a helicoidal curvature and to mount them upon the ends of arms to increase theirradius. A rearward projec tion may also be formed upon each of the blades, which, under some modifications of 'the invention, is found to aid in restricting the impulse imparted to the water to a longithe line of motion of the vessel.

It is believed that the most effective shape of propelling-blade is produced by forming it with a center of concavity at or near the forward or cutting edge and at about the center of the said edge. From this point the surface has a curvature of about equal radius in each direction-inward, outward, and rearwardfor a certain distance, beyond which the curvature varies in blades of different outline. Blades designed for rapid motion have their greatestlength'in a direction radial to the shaft. Blades designed to exert great power with comparativelyslow movement are longer in a direction perpendicular to the radius. The helicoidal-bladed screw and blades of simple spiral form lose much of their effectiveness by reason of lateral displacement of the water.

This fact is demonstrated by the extent by.

which the water is moved by such screws in lines divergent from that of the vessels motion. By constructing the blades in concav'o: convex formit is found that the screw is adapted to impel the water in a line coincident with that of the motion of the vessel,

and it has been found practicable to combine this eoneavo-convexitywith a helicoidal curvature, so as to avail the well-known effective and easy rotation of the helicoidal bladed screw.

The invention admits of embodiment under a variety of modified forms, some of which will be described for the purpose of illustration.

In the accompanying drawings,Figure l is an elevation of the working face of a screwpropeller illustrating the invention. Fig. 2 is a section of one of the blades on the line w w, Fig. 1. Fig. 3. is an elevation of the working face of a screw-propeller with blades possessin g similar characteristics, but modified in form and proportion. Fig. 4 is a longitudinal section of one of the blades on the line as, Fig. 3. Fig. 5 is a transverse section thereof on the line y y, Fig. 3. Figs. 6 and 7 are, respectively, a face view and a rear View of another modification.

In all the figures, a is the front or cutting edge of the blade,and b the back edge considered in respect to its forward rotation. c is the point of central concavity on the face of the blade, which, it will be observed, is, inmost of the modifications, located at or near the cutting-edge. The term center of concavity may be defined as a point from which the surface has a curvature of equal pitch or radius in each direction-in ward, outward, and rearward, as illustrated by radial lines fin Fig. lfor some distance, as, for example, to

the line g, Fig. 1. Locating this point 0 at or near the cutting-edge of the blade prevents pressure being produced on the back of the blade, either by the rotary movement of the screw or by the forward movement of the vessel through the water.

The invention also admits of combining the advantages of a concavo-convex form, which perfectly prevents the imparting of lateral or tangential motion to the water, with a helicoidal form in the entire blade, which is th most effective shape for propulsion. The concavo-convex blades may be connected directly to the hub d, but it is preferred to form them with arms, 6, of any desired length.

The propeller may consist of two, three, or four blades, and may be cast in one piece or separately, as preferred. The most advantageous angle of the blade with the plane of motion willvary according to speed, and will be determined by experiment. In Fig. 1, which illustrates the preferred form of the invention, the periphery or outer edge of each blade is concentric (or nearly so) with the axis of rotation. The propeller under its various modifications is well adapted for propelling vessels and boats of all descriptions upon sea or river. It is also valuable for propulsion on canals, the purely longitudinal movement of the water guarding effectually against washing the banks. The effect of the improved screw in moving the water directly aft greatly reduces the labor of steering, and increases the efliciency of the rudder.

Witnesses Oornvrus KNIGHT, WALTER ALLEN. 

